A conventional dumbbell assembly 50 is shown in FIG. 5 and generally includes a rod 51 and multiple disk-like weight members 52 connected to two ends of the rod 51. The rod 51 includes two threaded ends 511 and the weight members 52 are mounted to the two threaded ends 511 and two nuts are respectively and threadedly connected to the threaded ends 511 to fix the weight members 52.
Although the number of the weight members can be adjusted, the dumbbell assembly can only be used to lift it up and down, which is so boring and the users easily give up.
The present invention intends to provide a dumbbell assembly which includes two wings rotatably connected to the rod and each wing is optionally connected to at least one weight members. The rod is rotatably received in a tube so that when using the dumbbell assembly, the wings rotate to apply centrifugal forces to the user's muscles.